Nokea
Immunity after single vaccination against tetanus - application of tetanus toxoid is:
- A. intense and usually life long
- B. of limited duration, booster vaccinations are needed
- C. infectious (non-sterile)
- D. no correct answer
Correct Answer: B
Rationale: The correct answer is B. Immunity after a single tetanus vaccination is of limited duration, usually around 10 years. Booster vaccinations are needed to maintain protection due to waning immunity over time. Choice A is incorrect as immunity is not usually lifelong. Choice C is incorrect as tetanus toxoid is a sterile vaccine and does not cause infection. Choice D is also incorrect as there is a correct answer, which is B.
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The cell envelope of Gram-negative bacteria is composed of:
- A. Cytoplasmic membrane, a peptidoglycan layer and an outer membrane
- B. Cytoplasmic membrane and peptidoglycan layer
- C. Only peptidoglycan layer
- D. None of the above
Correct Answer: A
Rationale: The correct answer is A because Gram-negative bacteria have a unique cell envelope structure consisting of a cytoplasmic membrane, a peptidoglycan layer, and an outer membrane. The cytoplasmic membrane is the innermost layer that separates the cytoplasm from the external environment. The peptidoglycan layer provides structural support to the cell. The outer membrane acts as an additional protective barrier and contains lipopolysaccharides. Choice B is incorrect because Gram-negative bacteria have an outer membrane in addition to the cytoplasmic membrane and peptidoglycan layer. Choice C is incorrect because Gram-negative bacteria have more than just a peptidoglycan layer in their cell envelope. Choice D is incorrect as the cell envelope of Gram-negative bacteria does have specific components.
A patient suffers from severe postoperative pseudomonadous infection. What of the following antibiotics should be administered in this case?
- A. Amicacin sulfate
- B. Benzylpenicillin
- C. Cephazolin
- D. Erythromycin
Correct Answer: A
Rationale: The correct answer is A: Amikacin sulfate. Pseudomonas aeruginosa is commonly resistant to many antibiotics, but aminoglycosides like Amikacin have good activity against it. Step 1: Identify the pathogen causing the infection. Step 2: Consider the antibiotic's spectrum of activity against the pathogen. Step 3: Choose an antibiotic with proven efficacy. Amikacin is a good choice due to its effectiveness against Pseudomonas. Choice B, Benzylpenicillin, is a penicillin which is not effective against Pseudomonas. Choice C, Cephazolin, is a cephalosporin with limited activity against Pseudomonas. Choice D, Erythromycin, is a macrolide which is not effective against Pseudomonas.
A patient with fever and sore throat had a throat culture revealing Gram-positive cocci in chains. The bacteria were catalase-negative and beta-hemolytic. What is the most likely causative agent?
- A. Streptococcus pyogenes
- B. Streptococcus pneumoniae
- C. Enterococcus faecalis
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pyogenes.
1. Gram-positive cocci in chains: characteristic of Streptococcus species.
2. Catalase-negative: Streptococcus species are catalase-negative.
3. Beta-hemolytic: S. pyogenes is beta-hemolytic on blood agar.
Therefore, S. pyogenes fits all these criteria.
B: Streptococcus pneumoniae is catalase-negative but alpha-hemolytic, not beta-hemolytic.
C: Enterococcus faecalis is catalase-negative, but not typically beta-hemolytic or in chains.
D: Staphylococcus aureus is catalase-positive and not in chains.
A sputum smear from a patient with pneumonia revealed Gram-positive cocci in pairs with pointed ends and capsules. What is the likely microorganism?
- A. Streptococcus pneumoniae
- B. Staphylococcus aureus
- C. Klebsiella pneumoniae
- D. Neisseria meningitidis
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pneumoniae. The description of Gram-positive cocci in pairs with pointed ends and capsules matches the morphology of S. pneumoniae. This bacterium is known to cause pneumonia, especially in individuals with underlying conditions like COPD. Staphylococcus aureus (B) typically appears in clusters, not pairs. Klebsiella pneumoniae (C) is a Gram-negative rod, not a cocci. Neisseria meningitidis (D) is a Gram-negative diplococcus, not a cocci. Hence, based on the morphology and clinical context, Streptococcus pneumoniae is the likely microorganism causing pneumonia in this patient.
A patient's sputum was stained using Ziehl-Neelsen method, which revealed red-colored bacilli on a blue background. What structural component of the cell is responsible for this staining property?
- A. Mycolic acid
- B. Capsule
- C. Flagella
- D. Endospores
Correct Answer: A
Rationale: The correct answer is A: Mycolic acid. Ziehl-Neelsen method is used to stain acid-fast bacteria, such as Mycobacterium species. Mycolic acid in the cell wall of these bacteria resists decolorization, leading to red-colored bacilli on a blue background. Capsule, flagella, and endospores do not play a role in this staining property. Capsules are usually stained using special techniques, flagella are not typically visible with this stain, and endospores are stained using the Schaeffer-Fulton method.